1. Field of Ivention
This invention relates to improvements in methods and apparatuses for dynamic information storage or retrieval, and more particularly to improvements in methods and circuitry for detecting electrical resistance in electronic components, especially for detecting faults in a write head of mass data storage devices, hard disk drives, or the like, particularly when the write head has an open fault while its electrical resistance is still relatively small.
2. Relevant Background
Mass data storage devices include tape drives, as well as hard disk drives that have one or more spinning magnetic disks or platters onto which data is recorded for storage and subsequent retrieval. Hard disk drives may be used in many applications, including personal computers, set top boxes, video and television applications, audio applications, or some mix thereof. Many applications are still being developed. Applications for hard disk drives are increasing in number, and are expected to further increase in the future.
Typically, mass data storage devices include a data transducer, or head, that is used to read data from and write data to a rotating magnetic media, usually in the form of a disk or platter on which a material containing orientable magnetic domains is carried. The write head portion of the head mechanism of the type to which the present invention pertains has a coil through which write currents are passed to create a magnetic field adjacent the disk to selectively orient the magnetic domains of the magnetic material on the disk. The impedance of the coil is generally in the range of between about 15 and 30 ohms.
Sometimes, however, the head mechanisms experience faults, the faults of interest herein being an open fault and a short fault. Efforts have been made to detect such open and short faults; however, such efforts have required relatively complicated circuitry, and generally have required a considerable impedance change in the open direction before the fault could be detected.
In the past, circuits used to detect an open condition of the coil of the head included a circuit having first and second current paths with the coil connected between the control elements, for example, the bases, of the current controlling devices in each path. The output was applied to control the differential currents in a differential amplifier, which produced an output faultxe2x80x94indicating signal if the currents became unbalanced beyond a predetermined limit. The complicated circuit used generally required a detection threshold for an open head fault of over 3000 ohms. When an open head fault appeared with a head resistance between about 150 to 3000 ohms, the pre-existing technique could not properly detect the fault.
In the case of a short to ground, the coil was connected in series with a pair of central transistors that produce currents that are mirrored in respective outer current mirror transistors. When the coil was shorted to ground, the current in the central transistors became large, which was mirrored in the outer mirror transistors to provide an indication of the short.
What is needed, therefore, is a relatively simple circuit and method for detecting open and short conditions in a circuit element, such as a data transducer or head, in which the open fault condition can be detected at a selectable detection threshold slightly above the normal impedance of the head.
In light of the above, therefore, it is an object of the invention to provide an improved circuit and method for detecting an open condition in a circuit element, such as a data transducer or head, or the like.
One of the advantages of the circuit used in accordance with a preferred embodiment of the invention is that an open head condition can be selectively established at a lower detection threshold than that of circuits used heretofore.
Another advantage of the circuit used in accordance with a preferred embodiment of the invention is that a fewer part count is required to implement the circuit.
These and other objects, features and advantages of the invention will be apparent to those skilled in the art from the following detailed description of the invention, when read in conjunction with the accompanying drawings and appended claims.
According to a broad aspect of the invention, a circuit is provided for generating a signal indicating an impedance fault of an electrical component. The circuit includes a differential amplifier with the electrical component being connected as a load in a first leg thereof. An impedance element is provided in a second leg of the differential amplifier, and a pair of bipolar transistors are respectively connected in the first and second legs. The pair of bipolar transistors have a constant bias voltage applied to inputs thereof, and an output circuit is connected to an output node of the first leg of the differential amplifier.
According to another broad aspect of the invention, a circuit is provided for generating a signal indicating an impedance fault of an electrical component. The circuit includes means for providing differential amplification in first and second differential current legs, the electrical component being connected as a load in the first differential current leg. Means are also included for providing a matching impedance in the second differential current leg. Active amplifier means having a constant bias applied to inputs thereof are provided in the first and second differential current legs for providing differential amplification of currents in the first and second differential current legs. Output circuit means are connected to an output node of the first differential current leg for providing the signal indicating an impedance fault of the electrical component.
According to yet another broad aspect of the invention, a method is presented for generating a signal indicating an impedance fault of an electrical component connected as a load in a first current leg. The method includes differentially amplifying currents in respective the first current leg and a second current leg with a fixed amplification value. A matching impedance is provided for the electrical component in the second current leg, and an output amplifier is provided at an output node of the first current leg for providing the signal indicating an impedance fault of the electrical component.